The disadvantage of these silicone oil microemulsions lies in the high price for the required silicone oil surfactants.
Alternatively, mixtures of silicone surfactants and conventional surfactants that do not contain silicon can be used (US 2003/0040571 A1).
Also known are silicone oil microemulsions that do not use silicon-containing surfactants. In this case, the usual non-ionic or ionic surfactants or mixtures thereof are used (U.S. Pat. No. 6,013,683; U.S. Pat. No. 6,071,975). The disadvantage with these systems is that very high proportions of surfactants are required to maintain microemulsions.
It is also possible to use for the oil functional silicones that contain e.g. vinyl groups, Si—H, amino groups, Si—OH. The microemulsions can also be used as reaction media (EP 1 221 455 A1; U.S. Pat. No. 5,518,716; U.S. Pat. No. 5,661,215; U.S. Pat. No. 5,684,085; U.S. Pat. No. 6,207,781 B1; U.S. Pat. No. 6,201,091 B1; U.S. Pat. No. 5,017,297; U.S. Pat. No. 5,891,954).
The efficiency of the surfactants is expressed in the amount of a surfactant that is needed to mix a certain portion of oil in water or vice versa in the form of a microemulsion. Increasing efficiency thus also means widening the temperature window in which the microemulsion is stable.
However, undesired lamellar mesophases frequently occur in the technical formulation of microemulsions. Lamellar mesophases cause optical anisotropy and increased viscosity.
Temperature behavior represents another problem in the technical formulation of microemulsions. In particular, adding an additive generally leads to a shift of the monophase areas that are important for the technical application to other temperature ranges. These shifts can be on the order of magnitude of 10° C. or more. However, the consequence of this is that e.g. formulas must be altered in order to adapt them to the new temperature behavior that prevails in the monophase area.
In addition there is the need to achieve a formulation that is at least equally good while saving on surfactants. In addition to costs, saving on surfactants is also advantageous for ecological and health reasons. These requirements are particularly pronounced for silicone oil microemulsions because the silicone surfactants used in this case are expensive or very high concentrations of the conventional surfactants have to be used.
German patent application 198 39 054.8-41 discloses a method for increasing the efficiency of surfactants while simultaneously suppressing lamellar mesophases, a method for stabilizing the temperature behavior of the temperature of the monophase area for oil, water, and surfactant mixtures, a method for enlarging the structure size of emulsified liquid particles in microemulsions, and a method for reducing the interfacial surface tension of oil/water mixtures in which AB block copolymers having a water-soluble block A and a water-insoluble block B are added.